Feature Request: Add support for custom date formatting

[dustinStratis]

It would be beneficial to allow users to specify custom date formatting patterns beyond the built-in ones. This would increase flexibility and cater to specific regional or application needs.

[kluever]

@dustinStratis Can you expand on this a bit more? Which explicit date formats do you want formatters for? Does this have any interaction with other APIs in Guava, or are you just looking for a class w/ some DateTimeFormatters? Guava has mostly resisted the urge to add a new package like com.google.common.time in favor of both improving java.time as well as ThreeTenExtra

[kluever]

A colleague reminded me of https://github.com/google/mug/tree/master/mug/src/main/java/com/google/mu/time which is authored by another Googler (and Guava contributor), @fluentfuture --- that might serve your needs.